erations. If the belt reinforcing fiber, i.e., stress member, as well as the belt material, have high tensile strength no elongation, the belt will never be instrumental in absorbing the shock loads. This will result in sheared belt teeth. Therefore, consider this into consideration when how big is the tiniest pulley and the components for the belt and stress member are selected.

The choice of the pulley materials (metal vs. plastic material) is usually a matter of price, desired accuracy, inertia, color, magnetic properties and, above all, personal preference based on experiences. Plastic material pulleys with metallic inserts or steel hubs represent an excellent compromise.

PRECAUTIONS
The following precautions ought to be taken when installing all timing belt drives:

Timing belt set up ought to be a snug in shape, neither too restricted nor too loose. The positive hold of the belt eliminates the necessity for high initial tension. As a result, a belt, when set up with a snug suit (that is, not too taut) assures longer life, less bearing wear and quieter operation. Preloading (often the reason behind premature failure) is not required. When torque is normally unusually high, a loose belt may “leap teeth” on starting. In such a case, the tension should be increased gradually, until satisfactory procedure is attained. An excellent guideline for installation pressure is as shown in Figure 20, and the corresponding tensioning force is demonstrated in Table 9, both shown in SECTION 10 BELT TENSIONING. For widths other than shown, increase push proportionally to the belt width. Instrumentation for calculating belt tension is available. Consult the product portion of this catalog.

Be sure that shafts are parallel and pulleys are in alignment. On an extended center get, it is sometimes recommended to offset the driven pulley to pay for the tendency of the belt to perform against one flange.

On a long center drive, it is imperative that the belt sag isn’t large enough to permit tooth on the slack side to engage one’s teeth on the tight part.

It is necessary that the body supporting the pulleys be rigid at all times. A nonrigid framework causes variation in middle range and resulting belt slackness. This, subsequently, can lead to jumping of teeth – specifically under beginning load with shaft misalignment.

Although belt tension requires little attention after preliminary installation, provision ought to be designed for some middle distance adjustment for ease in installing and removing belts. Do not push belt over flange of pulley.

Idlers, either of the within or outdoors type, aren’t recommended and should not be used except for power takeoff or functional make use of. When an idler is necessary, it should be on the slack part of the belt. Inside idlers should be grooved, unless their diameters are higher than an equivalent 40-groove pulley. Flat idlers should not be crowned (use edge flanges). Idler diameters must exceed the tiniest diameter travel pulley. Idler arc of contact should be kept to a minimum.

As well as the general suggestions enumerated previously, particular operating characteristics of the travel must be taken into account.